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1 | =head1 NAME |
2 | |
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3 | perlfaq9 - Networking ($Revision: 1.26 $, $Date: 1999/05/23 16:08:30 $) |
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4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | This section deals with questions related to networking, the internet, |
8 | and a few on the web. |
9 | |
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10 | =head2 My CGI script runs from the command line but not the browser. (500 Server Error) |
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11 | |
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12 | If you can demonstrate that you've read the following FAQs and that |
13 | your problem isn't something simple that can be easily answered, you'll |
14 | probably receive a courteous and useful reply to your question if you |
15 | post it on comp.infosystems.www.authoring.cgi (if it's something to do |
16 | with HTTP, HTML, or the CGI protocols). Questions that appear to be Perl |
17 | questions but are really CGI ones that are posted to comp.lang.perl.misc |
18 | may not be so well received. |
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19 | |
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20 | The useful FAQs and related documents are: |
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21 | |
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22 | CGI FAQ |
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23 | http://www.webthing.com/page.cgi/cgifaq |
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24 | |
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25 | Web FAQ |
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26 | http://www.boutell.com/faq/ |
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27 | |
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28 | WWW Security FAQ |
29 | http://www.w3.org/Security/Faq/ |
30 | |
31 | HTTP Spec |
32 | http://www.w3.org/pub/WWW/Protocols/HTTP/ |
33 | |
34 | HTML Spec |
35 | http://www.w3.org/TR/REC-html40/ |
36 | http://www.w3.org/pub/WWW/MarkUp/ |
37 | |
38 | CGI Spec |
39 | http://www.w3.org/CGI/ |
40 | |
41 | CGI Security FAQ |
42 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt |
43 | |
44 | =head2 How can I get better error messages from a CGI program? |
45 | |
46 | Use the CGI::Carp module. It replaces C<warn> and C<die>, plus the |
47 | normal Carp modules C<carp>, C<croak>, and C<confess> functions with |
48 | more verbose and safer versions. It still sends them to the normal |
49 | server error log. |
50 | |
51 | use CGI::Carp; |
52 | warn "This is a complaint"; |
53 | die "But this one is serious"; |
54 | |
55 | The following use of CGI::Carp also redirects errors to a file of your choice, |
56 | placed in a BEGIN block to catch compile-time warnings as well: |
57 | |
58 | BEGIN { |
59 | use CGI::Carp qw(carpout); |
60 | open(LOG, ">>/var/local/cgi-logs/mycgi-log") |
61 | or die "Unable to append to mycgi-log: $!\n"; |
62 | carpout(*LOG); |
63 | } |
64 | |
65 | You can even arrange for fatal errors to go back to the client browser, |
66 | which is nice for your own debugging, but might confuse the end user. |
67 | |
68 | use CGI::Carp qw(fatalsToBrowser); |
69 | die "Bad error here"; |
70 | |
71 | Even if the error happens before you get the HTTP header out, the module |
72 | will try to take care of this to avoid the dreaded server 500 errors. |
73 | Normal warnings still go out to the server error log (or wherever |
74 | you've sent them with C<carpout>) with the application name and date |
75 | stamp prepended. |
76 | |
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77 | =head2 How do I remove HTML from a string? |
78 | |
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79 | The most correct way (albeit not the fastest) is to use HTML::Parser |
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80 | from CPAN (part of the HTML-Tree package on CPAN). |
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81 | |
82 | Many folks attempt a simple-minded regular expression approach, like |
83 | C<s/E<lt>.*?E<gt>//g>, but that fails in many cases because the tags |
84 | may continue over line breaks, they may contain quoted angle-brackets, |
85 | or HTML comment may be present. Plus folks forget to convert |
86 | entities, like C<<> for example. |
87 | |
88 | Here's one "simple-minded" approach, that works for most files: |
89 | |
90 | #!/usr/bin/perl -p0777 |
91 | s/<(?:[^>'"]*|(['"]).*?\1)*>//gs |
92 | |
93 | If you want a more complete solution, see the 3-stage striphtml |
94 | program in |
95 | http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/striphtml.gz |
96 | . |
97 | |
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98 | Here are some tricky cases that you should think about when picking |
99 | a solution: |
100 | |
101 | <IMG SRC = "foo.gif" ALT = "A > B"> |
102 | |
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103 | <IMG SRC = "foo.gif" |
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104 | ALT = "A > B"> |
105 | |
106 | <!-- <A comment> --> |
107 | |
108 | <script>if (a<b && a>c)</script> |
109 | |
110 | <# Just data #> |
111 | |
112 | <![INCLUDE CDATA [ >>>>>>>>>>>> ]]> |
113 | |
114 | If HTML comments include other tags, those solutions would also break |
115 | on text like this: |
116 | |
117 | <!-- This section commented out. |
118 | <B>You can't see me!</B> |
119 | --> |
120 | |
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121 | =head2 How do I extract URLs? |
122 | |
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123 | A quick but imperfect approach is |
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124 | |
125 | #!/usr/bin/perl -n00 |
126 | # qxurl - tchrist@perl.com |
127 | print "$2\n" while m{ |
128 | < \s* |
129 | A \s+ HREF \s* = \s* (["']) (.*?) \1 |
130 | \s* > |
131 | }gsix; |
132 | |
133 | This version does not adjust relative URLs, understand alternate |
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134 | bases, deal with HTML comments, deal with HREF and NAME attributes |
135 | in the same tag, understand extra qualifiers like TARGET, or accept |
136 | URLs themselves as arguments. It also runs about 100x faster than a |
137 | more "complete" solution using the LWP suite of modules, such as the |
138 | http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/xurl.gz program. |
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139 | |
140 | =head2 How do I download a file from the user's machine? How do I open a file on another machine? |
141 | |
142 | In the context of an HTML form, you can use what's known as |
143 | B<multipart/form-data> encoding. The CGI.pm module (available from |
144 | CPAN) supports this in the start_multipart_form() method, which isn't |
145 | the same as the startform() method. |
146 | |
147 | =head2 How do I make a pop-up menu in HTML? |
148 | |
149 | Use the B<E<lt>SELECTE<gt>> and B<E<lt>OPTIONE<gt>> tags. The CGI.pm |
150 | module (available from CPAN) supports this widget, as well as many |
151 | others, including some that it cleverly synthesizes on its own. |
152 | |
153 | =head2 How do I fetch an HTML file? |
154 | |
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155 | One approach, if you have the lynx text-based HTML browser installed |
156 | on your system, is this: |
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157 | |
158 | $html_code = `lynx -source $url`; |
159 | $text_data = `lynx -dump $url`; |
160 | |
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161 | The libwww-perl (LWP) modules from CPAN provide a more powerful way |
162 | to do this. They don't require lynx, but like lynx, can still work |
163 | through proxies: |
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164 | |
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165 | # simplest version |
166 | use LWP::Simple; |
167 | $content = get($URL); |
168 | |
169 | # or print HTML from a URL |
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170 | use LWP::Simple; |
171 | getprint "http://www.sn.no/libwww-perl/"; |
172 | |
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173 | # or print ASCII from HTML from a URL |
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174 | # also need HTML-Tree package from CPAN |
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175 | use LWP::Simple; |
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176 | use HTML::Parser; |
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177 | use HTML::FormatText; |
178 | my ($html, $ascii); |
179 | $html = get("http://www.perl.com/"); |
180 | defined $html |
181 | or die "Can't fetch HTML from http://www.perl.com/"; |
182 | $ascii = HTML::FormatText->new->format(parse_html($html)); |
183 | print $ascii; |
184 | |
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185 | =head2 How do I automate an HTML form submission? |
186 | |
187 | If you're submitting values using the GET method, create a URL and encode |
188 | the form using the C<query_form> method: |
189 | |
190 | use LWP::Simple; |
191 | use URI::URL; |
192 | |
193 | my $url = url('http://www.perl.com/cgi-bin/cpan_mod'); |
194 | $url->query_form(module => 'DB_File', readme => 1); |
195 | $content = get($url); |
196 | |
197 | If you're using the POST method, create your own user agent and encode |
198 | the content appropriately. |
199 | |
200 | use HTTP::Request::Common qw(POST); |
201 | use LWP::UserAgent; |
202 | |
203 | $ua = LWP::UserAgent->new(); |
204 | my $req = POST 'http://www.perl.com/cgi-bin/cpan_mod', |
205 | [ module => 'DB_File', readme => 1 ]; |
206 | $content = $ua->request($req)->as_string; |
207 | |
208 | =head2 How do I decode or create those %-encodings on the web? |
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209 | |
210 | Here's an example of decoding: |
211 | |
212 | $string = "http://altavista.digital.com/cgi-bin/query?pg=q&what=news&fmt=.&q=%2Bcgi-bin+%2Bperl.exe"; |
213 | $string =~ s/%([a-fA-F0-9]{2})/chr(hex($1))/ge; |
214 | |
215 | Encoding is a bit harder, because you can't just blindly change |
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216 | all the non-alphanumunder character (C<\W>) into their hex escapes. |
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217 | It's important that characters with special meaning like C</> and C<?> |
218 | I<not> be translated. Probably the easiest way to get this right is |
219 | to avoid reinventing the wheel and just use the URI::Escape module, |
220 | which is part of the libwww-perl package (LWP) available from CPAN. |
221 | |
222 | =head2 How do I redirect to another page? |
223 | |
224 | Instead of sending back a C<Content-Type> as the headers of your |
225 | reply, send back a C<Location:> header. Officially this should be a |
226 | C<URI:> header, so the CGI.pm module (available from CPAN) sends back |
227 | both: |
228 | |
229 | Location: http://www.domain.com/newpage |
230 | URI: http://www.domain.com/newpage |
231 | |
232 | Note that relative URLs in these headers can cause strange effects |
233 | because of "optimizations" that servers do. |
234 | |
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235 | $url = "http://www.perl.com/CPAN/"; |
236 | print "Location: $url\n\n"; |
237 | exit; |
238 | |
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239 | To target a particular frame in a frameset, include the "Window-target:" |
240 | in the header. |
241 | |
242 | print <<EOF; |
243 | Location: http://www.domain.com/newpage |
244 | Window-target: <FrameName> |
245 | |
246 | EOF |
247 | |
248 | To be correct to the spec, each of those virtual newlines should really be |
249 | physical C<"\015\012"> sequences by the time you hit the client browser. |
250 | Except for NPH scripts, though, that local newline should get translated |
251 | by your server into standard form, so you shouldn't have a problem |
252 | here, even if you are stuck on MacOS. Everybody else probably won't |
253 | even notice. |
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254 | |
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255 | =head2 How do I put a password on my web pages? |
256 | |
257 | That depends. You'll need to read the documentation for your web |
258 | server, or perhaps check some of the other FAQs referenced above. |
259 | |
260 | =head2 How do I edit my .htpasswd and .htgroup files with Perl? |
261 | |
262 | The HTTPD::UserAdmin and HTTPD::GroupAdmin modules provide a |
263 | consistent OO interface to these files, regardless of how they're |
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264 | stored. Databases may be text, dbm, Berkley DB or any database with a |
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265 | DBI compatible driver. HTTPD::UserAdmin supports files used by the |
266 | `Basic' and `Digest' authentication schemes. Here's an example: |
267 | |
268 | use HTTPD::UserAdmin (); |
269 | HTTPD::UserAdmin |
270 | ->new(DB => "/foo/.htpasswd") |
271 | ->add($username => $password); |
272 | |
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273 | =head2 How do I make sure users can't enter values into a form that cause my CGI script to do bad things? |
274 | |
275 | Read the CGI security FAQ, at |
276 | http://www-genome.wi.mit.edu/WWW/faqs/www-security-faq.html, and the |
277 | Perl/CGI FAQ at |
278 | http://www.perl.com/CPAN/doc/FAQs/cgi/perl-cgi-faq.html. |
279 | |
280 | In brief: use tainting (see L<perlsec>), which makes sure that data |
281 | from outside your script (eg, CGI parameters) are never used in |
282 | C<eval> or C<system> calls. In addition to tainting, never use the |
283 | single-argument form of system() or exec(). Instead, supply the |
284 | command and arguments as a list, which prevents shell globbing. |
285 | |
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286 | =head2 How do I parse a mail header? |
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287 | |
288 | For a quick-and-dirty solution, try this solution derived |
289 | from page 222 of the 2nd edition of "Programming Perl": |
290 | |
291 | $/ = ''; |
292 | $header = <MSG>; |
293 | $header =~ s/\n\s+/ /g; # merge continuation lines |
294 | %head = ( UNIX_FROM_LINE, split /^([-\w]+):\s*/m, $header ); |
295 | |
296 | That solution doesn't do well if, for example, you're trying to |
297 | maintain all the Received lines. A more complete approach is to use |
298 | the Mail::Header module from CPAN (part of the MailTools package). |
299 | |
300 | =head2 How do I decode a CGI form? |
301 | |
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302 | You use a standard module, probably CGI.pm. Under no circumstances |
303 | should you attempt to do so by hand! |
304 | |
305 | You'll see a lot of CGI programs that blindly read from STDIN the number |
306 | of bytes equal to CONTENT_LENGTH for POSTs, or grab QUERY_STRING for |
307 | decoding GETs. These programs are very poorly written. They only work |
308 | sometimes. They typically forget to check the return value of the read() |
309 | system call, which is a cardinal sin. They don't handle HEAD requests. |
310 | They don't handle multipart forms used for file uploads. They don't deal |
311 | with GET/POST combinations where query fields are in more than one place. |
312 | They don't deal with keywords in the query string. |
313 | |
314 | In short, they're bad hacks. Resist them at all costs. Please do not be |
315 | tempted to reinvent the wheel. Instead, use the CGI.pm or CGI_Lite.pm |
316 | (available from CPAN), or if you're trapped in the module-free land |
317 | of perl1 .. perl4, you might look into cgi-lib.pl (available from |
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318 | http://cgi-lib.stanford.edu/cgi-lib/ ). |
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319 | |
320 | Make sure you know whether to use a GET or a POST in your form. |
321 | GETs should only be used for something that doesn't update the server. |
322 | Otherwise you can get mangled databases and repeated feedback mail |
323 | messages. The fancy word for this is ``idempotency''. This simply |
324 | means that there should be no difference between making a GET request |
325 | for a particular URL once or multiple times. This is because the |
326 | HTTP protocol definition says that a GET request may be cached by the |
327 | browser, or server, or an intervening proxy. POST requests cannot be |
328 | cached, because each request is independent and matters. Typically, |
329 | POST requests change or depend on state on the server (query or update |
330 | a database, send mail, or purchase a computer). |
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331 | |
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332 | =head2 How do I check a valid mail address? |
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333 | |
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334 | You can't, at least, not in real time. Bummer, eh? |
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335 | |
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336 | Without sending mail to the address and seeing whether there's a human |
337 | on the other hand to answer you, you cannot determine whether a mail |
338 | address is valid. Even if you apply the mail header standard, you |
339 | can have problems, because there are deliverable addresses that aren't |
340 | RFC-822 (the mail header standard) compliant, and addresses that aren't |
341 | deliverable which are compliant. |
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342 | |
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343 | Many are tempted to try to eliminate many frequently-invalid |
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344 | mail addresses with a simple regex, such as |
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345 | C</^[\w.-]+\@([\w.-]\.)+\w+$/>. It's a very bad idea. However, |
346 | this also throws out many valid ones, and says nothing about |
347 | potential deliverability, so is not suggested. Instead, see |
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348 | http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/ckaddr.gz , |
349 | which actually checks against the full RFC spec (except for nested |
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350 | comments), looks for addresses you may not wish to accept mail to |
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351 | (say, Bill Clinton or your postmaster), and then makes sure that the |
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352 | hostname given can be looked up in the DNS MX records. It's not fast, |
353 | but it works for what it tries to do. |
354 | |
355 | Our best advice for verifying a person's mail address is to have them |
356 | enter their address twice, just as you normally do to change a password. |
357 | This usually weeds out typos. If both versions match, send |
358 | mail to that address with a personal message that looks somewhat like: |
359 | |
360 | Dear someuser@host.com, |
361 | |
362 | Please confirm the mail address you gave us Wed May 6 09:38:41 |
363 | MDT 1998 by replying to this message. Include the string |
364 | "Rumpelstiltskin" in that reply, but spelled in reverse; that is, |
365 | start with "Nik...". Once this is done, your confirmed address will |
366 | be entered into our records. |
367 | |
368 | If you get the message back and they've followed your directions, |
369 | you can be reasonably assured that it's real. |
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370 | |
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371 | A related strategy that's less open to forgery is to give them a PIN |
372 | (personal ID number). Record the address and PIN (best that it be a |
373 | random one) for later processing. In the mail you send, ask them to |
374 | include the PIN in their reply. But if it bounces, or the message is |
375 | included via a ``vacation'' script, it'll be there anyway. So it's |
376 | best to ask them to mail back a slight alteration of the PIN, such as |
377 | with the characters reversed, one added or subtracted to each digit, etc. |
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378 | |
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379 | =head2 How do I decode a MIME/BASE64 string? |
380 | |
381 | The MIME-tools package (available from CPAN) handles this and a lot |
382 | more. Decoding BASE64 becomes as simple as: |
383 | |
384 | use MIME::base64; |
385 | $decoded = decode_base64($encoded); |
386 | |
387 | A more direct approach is to use the unpack() function's "u" |
388 | format after minor transliterations: |
389 | |
390 | tr#A-Za-z0-9+/##cd; # remove non-base64 chars |
391 | tr#A-Za-z0-9+/# -_#; # convert to uuencoded format |
392 | $len = pack("c", 32 + 0.75*length); # compute length byte |
393 | print unpack("u", $len . $_); # uudecode and print |
394 | |
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395 | =head2 How do I return the user's mail address? |
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396 | |
397 | On systems that support getpwuid, the $E<lt> variable and the |
398 | Sys::Hostname module (which is part of the standard perl distribution), |
399 | you can probably try using something like this: |
400 | |
401 | use Sys::Hostname; |
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402 | $address = sprintf('%s@%s', getpwuid($<), hostname); |
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403 | |
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404 | Company policies on mail address can mean that this generates addresses |
405 | that the company's mail system will not accept, so you should ask for |
406 | users' mail addresses when this matters. Furthermore, not all systems |
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407 | on which Perl runs are so forthcoming with this information as is Unix. |
408 | |
409 | The Mail::Util module from CPAN (part of the MailTools package) provides a |
410 | mailaddress() function that tries to guess the mail address of the user. |
411 | It makes a more intelligent guess than the code above, using information |
412 | given when the module was installed, but it could still be incorrect. |
413 | Again, the best way is often just to ask the user. |
414 | |
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415 | =head2 How do I send mail? |
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416 | |
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417 | Use the C<sendmail> program directly: |
418 | |
419 | open(SENDMAIL, "|/usr/lib/sendmail -oi -t -odq") |
420 | or die "Can't fork for sendmail: $!\n"; |
421 | print SENDMAIL <<"EOF"; |
422 | From: User Originating Mail <me\@host> |
423 | To: Final Destination <you\@otherhost> |
424 | Subject: A relevant subject line |
425 | |
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426 | Body of the message goes here after the blank line |
427 | in as many lines as you like. |
c8db1d39 |
428 | EOF |
429 | close(SENDMAIL) or warn "sendmail didn't close nicely"; |
430 | |
431 | The B<-oi> option prevents sendmail from interpreting a line consisting |
432 | of a single dot as "end of message". The B<-t> option says to use the |
433 | headers to decide who to send the message to, and B<-odq> says to put |
434 | the message into the queue. This last option means your message won't |
435 | be immediately delivered, so leave it out if you want immediate |
436 | delivery. |
437 | |
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438 | Alternate, less convenient approaches include calling mail (sometimes |
439 | called mailx) directly or simply opening up port 25 have having an |
440 | intimate conversation between just you and the remote SMTP daemon, |
441 | probably sendmail. |
442 | |
443 | Or you might be able use the CPAN module Mail::Mailer: |
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444 | |
445 | use Mail::Mailer; |
446 | |
447 | $mailer = Mail::Mailer->new(); |
448 | $mailer->open({ From => $from_address, |
449 | To => $to_address, |
450 | Subject => $subject, |
451 | }) |
452 | or die "Can't open: $!\n"; |
453 | print $mailer $body; |
454 | $mailer->close(); |
455 | |
456 | The Mail::Internet module uses Net::SMTP which is less Unix-centric than |
457 | Mail::Mailer, but less reliable. Avoid raw SMTP commands. There |
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458 | are many reasons to use a mail transport agent like sendmail. These |
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459 | include queueing, MX records, and security. |
460 | |
461 | =head2 How do I read mail? |
462 | |
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463 | While you could use the Mail::Folder module from CPAN (part of the |
464 | MailFolder package) or the Mail::Internet module from CPAN (also part |
465 | of the MailTools package), often a module is overkill, though. Here's a |
466 | mail sorter. |
467 | |
468 | #!/usr/bin/perl |
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469 | # bysub1 - simple sort by subject |
470 | my(@msgs, @sub); |
471 | my $msgno = -1; |
472 | $/ = ''; # paragraph reads |
473 | while (<>) { |
474 | if (/^From/m) { |
475 | /^Subject:\s*(?:Re:\s*)*(.*)/mi; |
476 | $sub[++$msgno] = lc($1) || ''; |
477 | } |
478 | $msgs[$msgno] .= $_; |
d92eb7b0 |
479 | } |
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480 | for my $i (sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msgs)) { |
481 | print $msgs[$i]; |
482 | } |
483 | |
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484 | Or more succinctly, |
c8db1d39 |
485 | |
486 | #!/usr/bin/perl -n00 |
487 | # bysub2 - awkish sort-by-subject |
488 | BEGIN { $msgno = -1 } |
489 | $sub[++$msgno] = (/^Subject:\s*(?:Re:\s*)*(.*)/mi)[0] if /^From/m; |
490 | $msg[$msgno] .= $_; |
491 | END { print @msg[ sort { $sub[$a] cmp $sub[$b] || $a <=> $b } (0 .. $#msg) ] } |
492 | |
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493 | =head2 How do I find out my hostname/domainname/IP address? |
494 | |
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495 | The normal way to find your own hostname is to call the C<`hostname`> |
496 | program. While sometimes expedient, this has some problems, such as |
497 | not knowing whether you've got the canonical name or not. It's one of |
498 | those tradeoffs of convenience versus portability. |
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499 | |
500 | The Sys::Hostname module (part of the standard perl distribution) will |
501 | give you the hostname after which you can find out the IP address |
502 | (assuming you have working DNS) with a gethostbyname() call. |
503 | |
504 | use Socket; |
505 | use Sys::Hostname; |
506 | my $host = hostname(); |
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507 | my $addr = inet_ntoa(scalar gethostbyname($host || 'localhost')); |
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508 | |
509 | Probably the simplest way to learn your DNS domain name is to grok |
510 | it out of /etc/resolv.conf, at least under Unix. Of course, this |
511 | assumes several things about your resolv.conf configuration, including |
512 | that it exists. |
513 | |
514 | (We still need a good DNS domain name-learning method for non-Unix |
515 | systems.) |
516 | |
517 | =head2 How do I fetch a news article or the active newsgroups? |
518 | |
519 | Use the Net::NNTP or News::NNTPClient modules, both available from CPAN. |
520 | This can make tasks like fetching the newsgroup list as simple as: |
521 | |
522 | perl -MNews::NNTPClient |
523 | -e 'print News::NNTPClient->new->list("newsgroups")' |
524 | |
525 | =head2 How do I fetch/put an FTP file? |
526 | |
527 | LWP::Simple (available from CPAN) can fetch but not put. Net::FTP (also |
528 | available from CPAN) is more complex but can put as well as fetch. |
529 | |
530 | =head2 How can I do RPC in Perl? |
531 | |
532 | A DCE::RPC module is being developed (but is not yet available), and |
533 | will be released as part of the DCE-Perl package (available from |
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534 | CPAN). The rpcgen suite, available from CPAN/authors/id/JAKE/, is |
535 | an RPC stub generator and includes an RPC::ONC module. |
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536 | |
537 | =head1 AUTHOR AND COPYRIGHT |
538 | |
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539 | Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. |
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540 | All rights reserved. |
541 | |
542 | When included as part of the Standard Version of Perl, or as part of |
543 | its complete documentation whether printed or otherwise, this work |
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544 | may be distributed only under the terms of Perl's Artistic License. |
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545 | Any distribution of this file or derivatives thereof I<outside> |
546 | of that package require that special arrangements be made with |
547 | copyright holder. |
548 | |
549 | Irrespective of its distribution, all code examples in this file |
550 | are hereby placed into the public domain. You are permitted and |
551 | encouraged to use this code in your own programs for fun |
552 | or for profit as you see fit. A simple comment in the code giving |
553 | credit would be courteous but is not required. |